Buffering agent delivery system for anesthetic syringe

ABSTRACT

A syringe for dispensing anesthetic from a cartridge having an interior wall defining a hollow interior sized and shaped for receiving a dose of anesthetic, and a piston. The syringe includes a tubular plunger slidably received in the hollow interior of the tubular cartridge. The plunger has a hollow interior extending between a distal end shaped for engaging the piston and an open proximal end. The syringe includes a plunger rod slidably received in the hollow interior of the tubular plunger. The rod has a sharp distal end adapted to penetrate the piston, a proximal end, and a length extending between the distal end and the proximal end sized so a delivery portion of the rod extends through the piston into the cartridge when the rod is driven through the piston. The delivery portion includes a recess for receiving a buffering agent to reduce acidity of the dose of anesthetic.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Patent Application 61/471,913filed Apr. 5, 2011, which is hereby incorporated by reference in itsentirety.

BACKGROUND

The present invention generally relates to syringes for injecting liquidmedications from prefilled cartridges, and more particularly to asyringe having a buffering agent delivery system for reducing theacidity of anesthetic.

Local anesthetic is frequently used to numb tissue in a patient's mouthto reduce pain and discomfort a patient may feel during a dentalprocedure. Conventionally, a reusable syringe assembly is used to injectthe anesthetic or medicine from a cartridge or carpule. The cartridge isa glass cylinder containing a local anesthetic and other ingredients. Adiaphragm at one end of the cylinder is held in place by an aluminumband. The opposite end of the cylinder has a moveable piston or stopper.The syringe assembly includes a barrel for receiving the cartridge, aplunger rod slidably received in a proximal end of the barrel foractuating the cartridge, an access needle at a distal end of the barrelfor puncturing the diaphragm, and a delivery needle connected to theaccess needle for delivering anesthetic to the patient. In some cases,the plunger rod includes a harpoon for engaging the piston.

Typically, the diaphragm of the cartridge is swabbed with alcohol beforebeing loaded into a pre-sterilized syringe. As the cartridge is loadedinto the syringe, the access needle extending proximally from the distalend of the barrel pierces the cartridge diaphragm so the anesthetic inthe cartridge can be dispensed. Once the cartridge is in place, theplunger rod of the syringe pushes the piston of the cartridge toward thediaphragm, forcing anesthetic through the access needle, into thedelivery needle, and ultimately into the patient.

Frequently, a topical anesthetic is used to reduce pain caused by theentry of the needle into the tissue and the delivery of the medicine.Among the properties that make anesthetic delivery painful is itsacidity. Local anesthetic solutions containing vasopressors (e.g.,epinephrine) are intentionally manufactured with lower pH (3-4 pH) toslow the oxidation of the vasopressor prolonging its effectiveness andthereby extending the shelf life of the drug. Thus, there is a need fora device that delivers effective anesthetic having a reduced acidity,without affecting the shelf life of the drug.

The present invention relates to a dental syringe for dispensinganesthetic from a cartridge having an interior wall defining a hollowinterior sized and shaped for receiving a dose of anesthetic, and apiston. The syringe comprises a tubular plunger slidably received in thehollow interior of the tubular barrel. The plunger has a hollow interiorextending between a distal end shaped for engaging the piston and anopen proximal end opposite the distal end. In addition, the syringeincludes a plunger rod slidably received in the hollow interior of thetubular plunger. The rod has a sharp distal end adapted to penetrate theseal, a proximal end, and a length extending between the distal end andthe proximal end sized so that a delivery portion of the rod extendsthrough the piston into the cartridge when the rod is driven through thepiston. The delivery portion includes a recess for receiving a bufferingagent to reduce an acidity of the dose of anesthetic.

SUMMARY

In one aspect, the present invention includes a syringe for dispensinganesthetic from a cartridge having an interior wall defining a hollowinterior sized and shaped for receiving a dose of anesthetic, and apiston. The syringe comprises a tubular plunger slidably received in thehollow interior of the tubular cartridge. The plunger has a hollowinterior extending between a distal end shaped for engaging the pistonand an open proximal end opposite the distal end. The syringe has aplunger rod slidably received in the hollow interior of the tubularplunger. The rod has a sharp distal end adapted to penetrate the piston,a proximal end, and a length extending between the distal end and theproximal end sized so that a delivery portion of the rod extends throughthe piston into the cartridge when the rod is driven through the piston.The delivery portion includes a recess for receiving a buffering agentto reduce an acidity of the dose of anesthetic.

In another aspect, the present invention includes a syringe andcartridge system comprising a cartridge having an interior wall defininga hollow interior sized and shaped for receiving a dose of anesthetic,and a piston slidably engaging the interior wall. The piston has adistal face facing the dose of anesthetic in the hollow interior of thecartridge, a proximal face opposite the distal face, a recess in theproximal face for receiving a predetermined amount of buffering agent,and a sheet sealing the buffering agent in the recess. The syringe andcartridge system also includes a plunger rod having a sharp distal endadapted to penetrate the sheet and piston forming a hole through thepiston, the buffering agent entering the hollow interior of thecartridge to reduce acidity of the dose of anesthetic therein.

Other aspects of the present invention will be apparent in view of thefollowing description and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation in partial section of a syringe of thepresent invention;

FIG. 2 a is a cross section of a plunger rod of a first embodiment ofthe present invention prior to delivering buffering agent to acartridge;

FIG. 2 b is a cross section of the plunger rod of a first embodimentafter delivering buffering agent to the cartridge;

FIG. 3 is a cross section of a plunger rod and cartridge system of asecond embodiment; and

FIG. 4 is a cross section of a plunger rod of a third embodiment.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to FIG. 1, a dental syringe of a first embodiment of thepresent invention is generally designated in its entirety by thereference number 10. The dental syringe 10 generally comprises a tubularbarrel 12 and a plunger rod 14 slidably received in a head or proximalend 16 of the barrel. A needle 18 is connected to an outlet 20 of thesyringe at its distal end for dispensing anesthetic to tissue of apatient when the plunger rod 14 is forced distal.

A cartridge or carpule, generally designated by 30, loaded in a hollowinterior of the syringe barrel 12 holds the anesthetic before beingdispensed. The cartridge 30 includes a transparent cylinder 32 having aelastomeric diaphragm 34 held in place at its distal end 38 by a band40, and an elastomeric stopper or piston 42 positioned in a proximal end44 of the cylinder 32. The diaphragm 34 is pierced to put the anestheticin communication with the dispensing needle 18 of the syringe 10. Theplunger rod 14 of the syringe 10 engages the piston 42 and forces theanesthetic out of the cylinder 32 and through the dispensing needle 18.

As illustrated in FIG. 2 a, the plunger rod 14 includes a tubularplunger or guide 50 having a channel 52 that slideably receives a rod54. A distal end 56 of the rod 54 includes a sharp point 58 forpenetrating the piston 42 of the cartridge 30 as will be explained inmore detail below. A proximal end 60 of the rod 54 includes aconventional thumb ring 62 for driving the rod through the cartridgepiston 42. A cavity 64 is provided in the rod 54 near its distal end 56for holding a buffering agent B prior to delivering it to the cartridge.A detent 66 is provided on the rod 54 near the thumb ring 62 forconnecting the rod 54 to the guide 50 so they move in unison.

The distal end of the guide 50 includes a flange 70 sized for receipt inthe proximal end 44 of the cartridge 30 to center the rod 54 on thepiston 42. A proximal end 72 of the guide 50 also includes a flange 74for centering the guide in the syringe barrel 12. A groove 76 isprovided around the channel 52 adjacent the proximal end 72 forreceiving the detent 66 on the rod 54 to prevent movement between therod and the guide 50.

As will be appreciated by those skilled in the art, when the rod 54 isinitially advanced, the rod moves distally inside the guide 50 so thesharp point 58 pierces the piston 42 of the cartridge 30. As the rod 54advances farther, the cavity 64 enters the hollow interior of thecartridge 30 as shown in FIG. 2 b so the buffering agent B mixes withthe anesthetic in the cartridge, reducing the acidity of the anesthetic.Eventually, the detent 66 on the rod 54 engages the groove 76 in thechannel 52 of the guide 50 so the guide advances with the rod. As theguide 50 advances, it forces the piston 42 of the cartridge 30 distallyin the cylinder 32, dispensing the contents of the cartridge through aneedle extending through the diaphragm 34 of the cartridge. In addition,the detent 66 permits the piston 42 to be retracted by pulling back onthe thumb ring 62 to aspirate anesthetic from the tissue as will beappreciated by those skilled in the art. In another embodiment, theanesthetic in the cartridge 30 may be at a negative pressure (i.e., apartial vacuum) to allow the buffer in the rod to easily exit the rodand mix with the anesthetic in the cartridge.

FIG. 3 illustrates another embodiment of a cartridge, generallydesignated by 100. The cartridge 100 includes a transparent cylinder 102having an elastomeric diaphragm (not shown) held in place at its distalend by a band (not shown), and an elastomeric piston 110 positioned in aproximal end 112 of the cylinder 102. The piston 110 includes a cavity114 in its proximal face 116. The cavity 114 is filled with bufferingagent B and covered with a film 118 to retain the agent in the cavity.As further illustrated in FIG. 3, a plunger rod 120 of the secondembodiment has a sharp point 124 for penetrating the film 118 and thepiston 110. The rod 120 also includes a flange 126 immediately proximalto the sharp point 124 and a second larger flange or barb 128 positionedproximal to the first flange.

As will be appreciated by those skilled in the art, when the plunger rod120 is initially advanced, the rod moves distally so its sharp point 124pierces the film 118. Moving farther, the sharp point 124 of the rod 120pierces the piston 110. As the rod 120 is advanced still farther, thefirst flange 126 pushes the buffering agent B through the opening in thepiston 110 created by the sharp point 124. As in the first embodiment,the buffering agent B reduces the acidity of the anesthetic. Advancingthe rod 120 still farther engages the barb 128 with the piston 110,forcing it distally in the cylinder 102 to dispense the contents of thecartridge through a needle extending through the diaphragm (not shown)of the cartridge 100. The barb 128 permits the piston 110 to bewithdrawn, aspirating the tissue.

In a third embodiment illustrated in FIG. 4, a buffer delivery system200 comprises a tubular plunger 201 having a channel 202 extendingbetween a sharp point 204 at its distal end and a thumb ring 206 at itsproximal end. A rod 210 having a cavity 212 extends through the channel202. When the tubular plunger 201 is initially advanced, its sharp point204 pierces the piston 42. Once the piston 42 is pierced, the rod 210 isadvanced until the cavity 212 enters the interior of the cylinder 32dispensing the buffering agent into the anesthetic. A flange 220 onextends from a proximal end of the tubular plunger 201 to engage the rod210 when advanced. Alternatively, a flange (not shown) may be positionedat or near the distal end of the tubular plunger 201 to contact thepiston 42 to dispense the anesthetic. Barbs 222 at or near the distalend of the tubular plunger 201 may be configured to engage the piston 42to prevent separation from the piston during aspiration. Alternatively,barbs (not shown) may extend from rod 210 to engage piston 42.

Having described the invention in detail, it will be apparent thatmodifications and variations are possible without departing from thescope of the invention defined in the appended claims. It is understoodthat embodiments of the invention may be used to deliver a two componentdrug in which the combination or mixing of the two components or twodrugs is performed shortly before administration to the patient.

When introducing elements of the present invention or the preferredembodiment(s) thereof, the articles “a”, “an”, “the”, and “said” areintended to mean that there are one or more of the elements. The terms“comprising”, “including”, and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements.

As various changes could be made in the above constructions, products,and methods without departing from the scope of the invention, it isintended that all matter contained in the above description and shown inthe accompanying drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:
 1. A syringe for dispensing anesthetic from acartridge having an interior wall defining a hollow interior sized andshaped for receiving a dose of anesthetic, and a piston, the syringecomprising: a tubular plunger slidably received in the hollow interiorof the tubular cartridge, said plunger having a hollow interiorextending between a distal end shaped for engaging the piston and anopen proximal end opposite the distal end; and a plunger rod slidablyreceived in the hollow interior of the tubular plunger, the rod having asharp distal end adapted to penetrate the piston, a proximal end, and alength extending between the distal end and the proximal end sized sothat a delivery portion of the rod extends through the piston into thecartridge when the rod is driven through the piston, said deliveryportion including a recess for receiving a buffering agent to reduceacidity of the dose of anesthetic.
 2. A syringe as set forth in claim 1wherein the recess is located in a side of the plunger rod.
 3. A syringeas set forth in claim 2 wherein the recess is spaced from the sharpdistal end of the plunger rod.
 4. A syringe as set forth in claim 1wherein the recess is spaced from the sharp distal end of the plungerrod.
 5. A syringe as set forth in claim 1 wherein at least one of therod and the plunger includes a detent and at least another of the rodand the plunger includes a corresponding opening for receiving thedetent for retaining the relative position of the rod in the plunger. 6.A syringe as set forth in claim 5 wherein the rod includes a detent andthe plunger includes a corresponding opening for receiving the detentfor retaining the relative position of the rod in the plunger.